Scattering times in the two-dimensional electron gas of AlxGa1-xN/AlN/GaN heterostructures

Low-field Hall and Shubnikov-de Haas (SdH) measurements were performed on two-dimensional electron gas of Al0.24Ga0.76N/GaN and Al0.24Ga0.76N/AlN/GaN heterostructures at a low temperature. A dramatic improvement in electron mobility is observed in Al0.24Ga0.76N/AlN/GaN heterostructures with 1 and 2 nm thick AlN interlayers. A further increase in the AlN thickness degrades the transport behaviour. Transport and quantum scattering times were derived from the corresponding Hall mobility and the oscillatory part of the SdH signal. The ratio of the transport scattering time and the quantum scattering time increases from 3.87 in the heterostructure without the AlN interlayer to 14.34 with the 1 nm AlN interlayer and to 12.45 with the 2 nm AlN interlayer. A modified scattering calculation due to charged dislocation with a finite length suggests that dislocation related long-range scattering event tends to dominate both transport and quantum scattering times when a thin AlN interlayer is introduced.